Semiconductor devices typically have large numbers of electronic elements which need to be interconnected in order for the device to function. These electrical elements can be interconnected by forming a "bridge contact" or "strap" between the structures.
Prior attempts to form straps to electrically connect polysilicon trenches and diffusion regions separated by a dielectric included depositing conductive polysilicon, such as boron doped silicon, after the formation of implants within the diffusion regions. The polysilicon layer is then etched to define the material as a "strap" in order to electrically connect the diffusion and the polysilicon trench. However, this process experiences significant problems, many relating to the fact that the polysilicon etchant would often get beneath the implants or TiSi.sub.x and etch holes in the underlying silicon thereby causing leakage in the resulting semiconductor device. In order to avoid such problems more complex processes were devised in which formation of a strap was constructed utilizing the out-diffusion of boron. The exposed silicon areas of the polysilicon trench and diffusion region are doped with boron using ion implantation. A diffusion barrier is then applied over the doped areas, masked and etched to remove selected areas of the barrier. A continuous layer of polysilicon is deposited and boron is out-diffused into the polysilicon upon the highly doped areas. Wet etches are then utilized to remove those portions of the continuous layer of polysilicon which do not contain the diffused boron dopant; another etch also removes the diffusion barrier. The residual doped polysilicon forms an electrical connection between the polysilicon trench and the diffusion region.
The few reliable methods currently available for the formation of bridge contacts or straps involve complex processing sequences and significant cycle-time. In addition, due to the wide array of steps incorporated within such methods it is often difficult to fully integrate them into the processing sequence without experiencing problems. For example, the thermal budget of the integrated process often involves masking and etching steps which cause voiding in the polysilicon and lifting of the polycide in the gate stack. Such potential problems could be eliminated or reduced by utilizing a process having a shorter cycle-time, fewer steps and, more importantly, incorporating standard processing steps and materials.
In addition, in order to protect existing structures, present processes often require the use of a thick oxide cap on gate stacks. Unfortunately, however, the thicker the oxide cap, the more bias related problems associated with the device. Conversely, reducing the thickness of the oxide cap and, thus, height of the gate stack reduces bias related problems and improves line width control.
It is therefore an object of the present invention to provide a method for electrically connecting two electronic elements of a semiconductor device separated by a dielectric which incorporates standard processing techniques and materials. It is a further object of the present invention to provide such a method which is more efficient, having fewer processing steps and a shorter cycle-time. It is a further object to reduce bias related problems and improve line width control of the resulting devices. It is a further object of the present invention to create a more reliable semiconductor device by forming the strap without damaging electrical components and thereby preventing leakage, shorts, and other potential defects.